[Lldb-commits] [lldb] 1d8093e - [lldb] Consume the source of zero-sized DW_OP_piece operations (#219395)

[via lldb-commits]

Author: MrEven132
Date: 2026-10-31T14:36:46+08:00
New Revision: 1d8093ee01d3cee7f993fb7c0339e09221111a34

URL: https://github.com/llvm/llvm-project/commit/1d8093ee01d3cee7f993fb7c0339e09221111a34
DIFF: https://github.com/llvm/llvm-project/commit/1d8093ee01d3cee7f993fb7c0339e09221111a34.diff

LOG: [lldb] Consume the source of zero-sized DW_OP_piece operations (#219395)

`Evaluate_DW_OP_piece` returned early for a zero-sized piece before
removing
its source location from the expression stack. A later non-empty piece
could
then assemble the correct composite buffer while the stale source
remained on
the stack and was returned instead.

Consume the source stack entry when a zero-sized piece has one, while
still
contributing no bytes to the composite. Add a unit test covering a
zero-sized
register piece followed by a non-empty register piece.

Fixes #209099

Added: 
    

Modified: 
    lldb/source/Expression/DWARFExpression.cpp
    lldb/unittests/Expression/DWARFExpressionTest.cpp

Removed: 
    


################################################################################
diff  --git a/lldb/source/Expression/DWARFExpression.cpp b/lldb/source/Expression/DWARFExpression.cpp
index a76a23c25eb1f4..66c2a6bf6a4b60 100644
--- a/lldb/source/Expression/DWARFExpression.cpp
+++ b/lldb/source/Expression/DWARFExpression.cpp
@@ -1112,8 +1112,13 @@ static llvm::Error Evaluate_DW_OP_piece(EvalContext &eval_ctx,
   // Reset for the next piece.
   eval_ctx.loc_desc_kind = Memory;
 
-  if (piece_byte_size == 0)
+  if (piece_byte_size == 0) {
+    // A zero-sized piece contributes no data, but it still consumes its source
+    // location description.
+    if (!eval_ctx.stack.empty())
+      eval_ctx.stack.pop_back();
     return llvm::Error::success();
+  }
 
   Value curr_piece;
 

diff  --git a/lldb/unittests/Expression/DWARFExpressionTest.cpp b/lldb/unittests/Expression/DWARFExpressionTest.cpp
index 31e629967c6a28..0484f216e55abf 100644
--- a/lldb/unittests/Expression/DWARFExpressionTest.cpp
+++ b/lldb/unittests/Expression/DWARFExpressionTest.cpp
@@ -2304,6 +2304,22 @@ TEST_F(DWARFExpressionMockProcessTest, DW_OP_piece_file_addr) {
                        ExpectHostAddress({0x11, 0x22}));
 }
 
+TEST_F(DWARFExpressionMockProcessTest, DW_OP_piece_zero_size) {
+  TestContext test_ctx;
+  ASSERT_TRUE(CreateTestContext(&test_ctx, "i386-pc-linux",
+                                RegisterValue(uint32_t{0x44332211})));
+
+  ExecutionContext exe_ctx(test_ctx.process_sp);
+  MockDwarfDelegate delegate = MockDwarfDelegate::Dwarf5();
+
+  // The zero-sized r3 piece contributes no bytes, but it must still consume
+  // its register location before the four-byte r0 piece is assembled.
+  EXPECT_THAT_EXPECTED(
+      Evaluate({DW_OP_reg3, DW_OP_piece, 0, DW_OP_reg0, DW_OP_piece, 4}, {},
+               &delegate, &exe_ctx, test_ctx.reg_ctx_sp.get()),
+      ExpectHostAddress({0x11, 0x22, 0x33, 0x44}));
+}
+
 class DWARFExpressionMockProcessTestWithAArch
     : public DWARFExpressionMockProcessTest {
 public: